Field of the Invention
The present invention relates to a feedback methodology in the switching power supply, particularly to an information feedback system using a separating device.
Description of the Related Art
Due to the fact that internal elements of most electric devices require direct-current (DC) voltages, a power supply is used to convert alternating-current (AC) voltages or DC voltage into the DC voltages such that the electric device operate well. The power supply is divided into nonisolated power supplies and isolated switching power supplies. Isolated power supplier, with an inclusion of a power transformer, is used for most AC to DC, and some DC to DC converters, for safety and other performance considerations. There are various topologies for such converters; examples of such isolated converters topologies including Flyback, Forward, Qusai-Resonant, Full Bridge, Half-Bridge and Push-Pull.
Take Flyback power supply as an example. As shown in FIG. 1, an isolated power converter includes a transformer 10 having a primary side and a secondary side and an N-channel metal oxide semiconductor field effect transistor (NMOSFET) 12 connected to the primary side. The secondary side is connected with an operating system 14. An input high voltage VH is applied to the primary side. A voltage VG is periodically applied to the gate of the NMOSFET 12 to control the transfer of power from the primary side to the secondary side. When the NMOSFET 12 is turned on, the energy is stored in the transformer 10. As the NMOSFET 12 is turned off, the stored energy in the transformer 10 is discharged.
Isolated converters typically use optocoupler 16 for the secondary side to send information back to the primary side for controlling the output voltage, current and various conditions. The isolation by power transformer 10 is required for safety considerations, but this isolation prevents the direct information feedback from the secondary (output) side to the primary side (input). Traditionally, the secondary side information is passed through an optocoupler 16, which allows information to be passed through the isolation.
While the optocoupler 16 serves its purpose, it has a number of disadvantages listed below: (1) Relative slow response, typically takes many converter cycles for the corresponding optocoupler operation. Thus, slows the primary controller response, and impact the converter performance. (2) Only simple information can be transmitted through optocoupler due to it's slow speed. (3) Optocoupler is an added component, not in the power path.
To overcome the abovementioned problems, the present invention provides an information feedback methodology, so as to solve the afore-mentioned problems of the prior art.